1. Discussion with Gregor Kiczales at UBC
Ontology of AOP
Ontology is the study of what there is, an inventory of what exists. An ontological commitment is a commitment to an existence claim for certain entities.
Slides and the last one are Gregor’s
An ontology is, in simple terms, a collection of concepts with
relations among them plus constraints on the relations.
AO Mechanisms in Demeter

2. basis of crosscutting a join point model (JPM) has 3 critical elements
what are the join points
in AspectJ
points in runtime call graps members
means of identifying join points
signatures (plus …)
means of specifying semantics at join points
advice
define members
AO Mechanisms in Demeter

3. basis of crosscutting a join point model (JPM) has 3 critical elements
what are the join points
in AspectJ
points in runtime call graph
class members
means of identifying join points
pointcuts
member signatures (plus …)
means of specifying semantics at join points
advice
define members
dynamic JPM static JPM
AO Mechanisms in Demeter

4. range of AOP languages means of … join points JPM join points
identifying
specifying semantics at
AspectJ dynamic JPM
points in execution call, get, set…
signatures w/ wildcards & other properties of JPs
advice
static JPM
class members
signatures
add members
Composition Filters
message sends & receptions
signature & property based object queries
wrappers declarative (filters) imperative (advice)
Hyper/J
members
add, compose (and remove) members
Demeter traversals
when traversal reaches object or edge
class & edge names
define visit method
AO Mechanisms in Demeter

5. See next slide for changes to Demeter
range of AOP languages
means of … join points
add, compose (and remove) members
signatures
members
Hyper/J
add members
class members
static JPM
Demeter traversals
Composition Filters
AspectJ dynamic JPM
JPM
types
message sends & receptions
points in execution call, get, set…
join points
succinct traversal specs
signature & property based object queries
signatures w/ wildcards & other properties of JPs
identifying
generate traversals
wrappers declarative (filters) imperative (advice)
advice
specifying semantics at
See next slide for changes to Demeter
AO Mechanisms in Demeter

6. range of AOP languages means of … join points JPM join points
identifying
specifying semantics at
AspectJ dynamic JPM
points in execution call, get, set…
signatures w/ wildcards & other properties of JPs
advice
static JPM
class members
signatures
add members
DemeterJ, Demeter/C++
dynamic JPM
static JPM 1
static JPM 2
static JPM 3
when traversal reaches object or edge
visitor method signatures
traversal spec. s
class graph g
class names
class graph
visitor method bodies
s + g (result = traversal implementation)
class graph with tokens=grammar (result = parsing and printing implementation)
AO Mechanisms in Demeter

7. range of AOP languages means of … join points add members signatures
class members
static JPM DJ
dynamic JPM 1
dynamic JPM 2
dynamic JPM 3
AspectJ dynamic JPM
JPM
when traversal reaches object or edge (method traverse)
when traversal reaches object (methods fetch, gather, asList)
nodes in object graphs
points in execution call, get, set…
join points
visitor method signatures
source and targets of traversal
trav. spec. s
class graph g
object graph o
signatures w/ wildcards & other properties of JPs
identifying
visitor method bodies
method name (fetch, gather, asList)
s+g+o(result = traversal implementation = edges to traverse at nodes in object graph)
advice
specifying semantics at
AO Mechanisms in Demeter

8. Composing join point models
Traversal Spec JPM: In Demeter we use traversal specifications and the class graph to define a traversal implementation (either static or dynamic)
Visitor JPM: The result of Traversal Spec. JPM is used to define a second JPM:
The traversal implementation defines nodes and edge visits.
Visitor signatures define the nodes and edges where additional advice is needed: they are the means of identifying join points.
The means of specifying semantics at join points are the visitor bodies.
AO Mechanisms in Demeter

9. DJ: dynamic JPM 3
The join points are nodes in object graphs. They are not dynamic call graph join points nor class members!
The means of identifying the join points for a given object graph o are a strategy s and the class graph g. o must conform to g.
The means of specifying the semantics at the join points are again s and g. See paper with Mitch Wand for the formal details behind this JPM.
AO Mechanisms in Demeter

10. DemeterJ: static JPM 1
The means of identifying the join points and of specifying the semantics at the join points are the same.
The reason is that s+g both
select the classes that will get traversal semantics
determine the details of the traversal semantics
AO Mechanisms in Demeter

11. DemeterJ: static JPM 3
The means of identifying the join points (class members) is done by the class graph.
When we add tokens to the class graph we get a grammar that contains instructions for parsing and printing behavior.
A grammar is an aspect (external representation aspect): the adhoc implementation cuts across all classes.
AO Mechanisms in Demeter

12. AO design in UML [Clarke, Walker] Composition Patterns
static JPM (~ Hyper/J)
binds pattern to base code
UML class & interaction diagrams already crosscut
by-class vs. by-interaction organizations
foo
dynamic JPM (~ AspectJ)
what happens in pattern
bar
AO Mechanisms in Demeter

13. Masuhara/Kiczales Modeling Framework for AO Mechanisms
A and B: languages
X: result domain of weaving process
X[JP]: join points in X
A[ID], B[ID]: identify join points in X
A[Eff], B[Eff]: effecting semantics at jps
META: parameterize weaving process
AO Mechanisms in Demeter

14. Masuhara/Kiczales Modeling Framework for AO MechanismsX
X[JP] A
A[ID]
A[Eff] B
B[ID]
B[Eff]
META
AO Mechanisms in Demeter

15. Demeter static JPM 1: special case of Open ClassesX
Combined program
X[JP]
c declarations A
c declarations including the class graph
A[ID]
Method signatures
A[Eff] B
Traversal specifications
B[ID]
c names
B[Eff]
META
Traversal semantics: rules for translating traversal specifications to methods
Adds traversal methods
to a set of classes
AO Mechanisms in Demeter

16. Demeter static JPM 2: Open Classes
See paper.
AO Mechanisms in Demeter

17. Demeter static JPM 3: special case of Open ClassesX
Combined program
X[JP]
c declarations A
c declarations including the class graph
A[ID]
Method signatures
A[Eff] B
Class dictionary (class graph enhanced with tokens defining the syntax addition)
B[ID]
c names
B[Eff]
META
rules for translating class dictionary to parsing methods
Adds parsing methods
to a set of classes
AO Mechanisms in Demeter

18. Demeter dynamic JPM 1: special case of Pointcuts and AdviceX
Traversal execution
X[JP]
Arrival at each object and has-a edge A
Traversal methods
A[ID]
Method signatures
A[Eff]
Execute traversal method body B
Visitor method declarations (serves as advice)
B[ID]
Visitor method signatures (serves as pointcut)
B[Eff]
Execute visitor method bodies
META
none
Adds advice to traversal methods
AO Mechanisms in Demeter

19. Demeter dynamic JPM 2: special case of TRAV
For methods fetch, gather and asList: special advice
AO Mechanisms in Demeter

20. Demeter dynamic JPM 3 X X[JP] A A[ID] A[Eff] B B[ID] B[Eff] META
Object graphs
X[JP]
Nodes in object graphs A
Class graph
A[ID]
Class names
A[Eff] B
Traversal specification
B[ID]
B[Eff]
Edges to traverse at node in object graph
META
Rules for traversal order: depth-first, breadth-first, left-to-right, etc.
AO Mechanisms in Demeter

21. Mixes two models together
Demeter dynamic JPM 4: DJ with Functional Visitor X
Traversal execution with runtime control (Subtraversal.apply(..))
X[JP]
Arrival at each object (Functional Visitor only available to nodes) A
Regular Java Program (class/fields declarations)
A[ID]
Class/fields signatures
A[Eff]
Provide reachability (my understanding is to construct object graph conforming to the class graph) B
Traversal specification and visitor method declarations (including the default one: combine(..))
B[ID]
Visitor method signatures (or the built-in semantics, for the combine(..))
B[Eff]
Execute the visitor methods and compute and combine the values and provide the runtime control over the traversal(subset of the traversal graph computed from the traversal specification)
META
Mixes two models together

22. Demeter dynamic JPM 4: DJ with Functional VisitorX
Traversal execution with runtime control (Subtraversal.apply(..))
X[JP]
Arrival at each object (Functional Visitor only available to nodes) A
Regular Java Program defining traversals (class/fields declarations)
A[ID]
Method signatures
A[Eff]
Execute traversal method body B
Visitor method declarations (including the default method: combine(..))
B[ID]
Visitor method signatures (or the built-in semantics, for the combine(..))
B[Eff]
Execute the visitor methods and compute and combine the values and provide the runtime control over the traversal
META
Taken apart

23. Conclusions
The Modelling Framework by Masuhara/Kiczales nicely captures the different AO mechanisms worked on by the Demeter team.
AO Mechanisms in Demeter